Data Sheet Chapter 5

500-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
325A, Rev. 0 5-6
Switch the transmitter to Operate and
adjust the front panel power pot for a
100% Visual Power reading.
5.9 (A8) 2-Way Combiner Assembly
(1198-1010 CH. 2-4 or 1222-1002
CH. 5-6; Appendix C)
There are no adjustments to (A8) the
VHF combiner assembly.
Note: The bandpass filter is factory
swept and should not be tuned
without the proper equipment. Do
not attempt to tune the filters
without a sweep generator or,
preferably, a network analyzer. If
tuning is required, consult the
Axcera Field Support Department
before attempting to make any
adjustments.
5.10 (A9)
Bandpass Filter
Assemblies (1076291 through
1076293 & 1077130; Appendix C)
The input to the (A9) bandpass filter
assemblies is the output of the VHF
combiner assembly, which is the
combined output of the VHF amplifier
trays. The filter is made of aluminum
waveguide and has five resonant cavities.
The filter has five bolts for tuning
adjustments. The bandpass filter also
utilizes two integral traps at -4.5 MHz
and +9 MHz from F
V
. Refer to the
bandpass filter drawing for the location of
the adjustments.
To tune the filter, connect a sweep signal
to the input of the filter and adjust the
five tuning bolts for a 6-MHz bandwidth
and a flat-frequency response across the
desired band.
Note: The bandpass ripple should be
0.25 dB. The 6-MHz band should
also have a minimum of 20 dB return
loss across the pass band.
Table 5-1 contains typical values for the
bandpass filter.
Table 5-1. Bandpass Filter Typical Values
FREQUENCY INSERTION LOSS (DB) RETURN LOSS (DB)
F
V
-4.5 35
F
V
-0.5 20
F
V
0.8 20
F
a
0.8 20
F
V
+8.08 15
F
V
-9 30
2F
V
30
5.11 (A6 and A7) Low-Band VHF
Amplifier Tray (1198-1600; Appendix
C)
The (A6 and A7) low-band VHF amplifier
tray (1198-1600) has been adjusted at
the factory to meet all specifications,
including phase adjustment to match the
multiple trays in an amplifier array when
they are combined. The tray should not
need to be adjusted to attain normal
operation. Any adjustments to the boards
in this tray should be performed in the
Manual Gain position, with S1 on (A13)
the AGC control board (1142-1601) in
Manual. The idling current for the
amplifier boards are adjusted with no RF
drive applied. S1 should be in the Auto
AGC position for the normal operation of
the transmitter.
Connect a dummy load with a rating of a
least 500 watts to J2, the RF output jack
of the tray.